The posthumous publication of a book never completed by an author to his satisfaction may usually be dismissed as an act of family piety, or, less generously, as the scraping of the barrel. But not this one. The Invention of Scotland is uncommonly interesting. It is written with Hugh Trevor-Roper’s characteristic grace and pungency, and it is agreeably provocative.

Its theme is the part played by myth in creating the Idea of Scotland. The origins of any myth may be lost in the mists of antiquity. But national myths may also be the product of self-conscious invention, and therefore, in Trevor-Roper’s view, to a great extent fraudulent, requiring “a continuous capacity for invention, and its formalisation may be seen as a ritual adjustment, a formal accommodation of barbarism to civility”. He declares: “The whole history of Scotland has been coloured by myth, and that myth, in Scotland, is never driven out by reality, or by reason, but lingers on until another myth has been discovered, or elaborated, to replace it.”

This is an argument to which only a fool can take exception. Nations need their myths, just as individuals do, for it is the myth that provides us with the sense of our own identity. Some myths may be damaging: “In Germany, the ancient barbarians of the race were revived in all their savagery, during the later 19th century and the first half of the 20th, as models for modern politics.” The Scotch myths were altogether more benign — and more useful.

Trevor-Roper identifies three of them: the Political Myth, the Literary Myth and the Sartorial Myth.

The first is the least known today. It was elaborated by medieval historians and received its final form in the 16th century from George Buchanan, humanist and the finest Latin poet of the age — the greatest since ­Virgil, according to his contemporaries. It was devised in opposition to Geoffrey of ­Monmouth’s Anglo-Welsh myth of Brutus or Brut, the Trojan prince and father of the British people. Since this version of history gave Brut and his successors sovereignty over the whole island of Britain, it became necessary for ­patriotic Scots to find a means of trumping it. They did so by producing a Greek prince called Gaythelos (Gaedil Glas, “the name ­indicating he was a Gael”), who travelled to Egypt where he married Scota, a pharaoh’s daughter, and then, by way of sojourns in Spain and Ireland, arrived in Scotland in 333BC.

This was very satisfactory because it enabled the Scots, who were only one of the peoples of Scotland, alongside Picts and Britons, and indeed comparative­ly recent arr­ivals from Ireland, to take poss­ession of the whole history of Scotland. Lists of kings (all ­imaginary, dating from Fergus, son of Feuchar) were produced as evidence of this antiquity. In this way, the Scots established their right to independence, disproving the claims of English kings, notably Edward I, to sovereignty over Scotland.

Then Buchanan, drawing on the inventive pseudo-histories of his predecessors, John of Fordoun and Hector Boece, put the myth to immediate political purpose by demonstrating, to his own entire satisfaction, that the Scots had made a habit of deposing any of these kings who proved unsatisfactory. This justified the deposition of Mary Queen of Scots, whom he had come to hate, and was subsequently to prove immensely useful, Trevor-Roper says, to English Whigs in the 17th century.

The Literary Myth took the form of creating an ancient literature for the Scots. The ­poems of the bard Ossian, Englished by James Macpherson in the early 1760s, were held to demonstrate that Scotland had produced great literature when England was still sunk in barbarism, and were therefore a source of pride to the Edinburgh literati conscious of the loss of national independence. It was, of course, only possible for them to celebrate the noble savages of Highland Scotland after the failure of the Jacobite Risings and the subsequent repression of Highland customs had rendered Lowland Scotland, whose hero was the Duke of Cumberland, not Prince Charles Edward, safe from these barbarians. Macpherson’s Ossian was largely, but not wholly, fraudulent. He did draw on authentic Gaelic poetry (translated for him, Trevor-Roper suggests, by his cousin Macpherson of Strathmashie). Its authenticity was soon successfully challenged, by Samuel Johnson among others.

Yet, even when it was no longer possible to argue that Macpherson had done no more than translate ancient Gaelic poetry, it remained a matter of Scottish pride that Ossian had conquered Europe. Napoleon was one of its chief fans, reading it in Cesarotti’s Italian translation, which is still in print. In any case, it was no great matter when belief in Ossian had to be abandoned, because a new and greater myth-maker had appeared in the person of Sir Walter Scott.

He played a major part in popularising the Sartorial Myth, which has made tartan and the kilt the symbols of Scottish national identity. Much of this section of the book is familiar: that the kilt as we know it (the short kilt) was actually invented by an English entrepreneur, by the name of Rawlinson, as a more suitable garb for his workers, and that the so-called clan tartans are a 19th-century invention, owing much to a pair of frauds, the Sobieski Stuarts, who claimed to be the grandsons of Bonnie Prince Charlie, and on whom Trevor-Roper spends too much time. Scott’s part in the popularising of tartan was more important, and his intention clear. It was a means of reconciling Highland and Lowland, and of affirming a distinct Scottish identity within Britain — one which did not challenge the Union. For more than two centuries, it worked very well.

One may question Trevor-Roper on particular details, but two general points should be made. First, he writes of the Scots as Celtic and the English as Anglo-Saxon, which is no longer a tenable opinion; both are mongrel peoples. Second, he denies to the Anglo-­Saxons (that is, the English) the mythopoeic faculty. “All the myths of England come not from the Anglo-Saxons, but from the Celts,” he writes. Perhaps so, but the English adopted Brutus and his descendant Arthur and made these myths their own. They may also have imbibed the myth of Merrie England from Scott’s Ivanhoe. Moreover, in the 16th and early 17th centuries, they devised their own myths: of the fiercely Protestant sea dogs who destroyed imperial Spain (the credit for doing that should really go to the Dutch and the French); and the myth of the ancient (Saxon) constitution, later subjected to “the Norman yoke”, which English judges elaborated to justify opposition to Stuart “despotism”.

I doubt if the invention of the Whig version of history was entirely the work of Buchanan and other Scots historians. In short, this is an enlightening and entertaining work, but one misses its companion piece: The Invention of England.